1. Field of the Invention
The present invention relates to an image signal processing apparatus that detects an electronic watermark embedded in image data obtained by performing a photographing operation with a digital camera or the like.
2. Description of the Related Art
Digital image data obtained by performing a photographing operation with a digital camera are recorded in a recording medium such as a CF (compact flash) card. The digital image data are read from the recording medium into a hard disk device or a memory device in a personal computer and a specific application program is executed on the personal computer to display the digital image data on a display unit connected to the personal computer, which may be a display device or a projection device. There are also apparatuses in the known art that display a digital image directly read from a recording medium on a display device without necessitating the use of a personal computer. In addition, storage apparatuses that copy image data recorded in a portable recording medium such as a CF card into another recording medium which may be an MO or a CD-R and file the image data thus copied as well as simply read out image data and display the image data on a display device have been brought into practical application.
Digital image data which are handled as described above can be duplicated easily. For this reason, rigorous development efforts have been made in the area of electronic watermarking technology that may be employed for the protection of digital image data copyright. An electronic watermark is made by embedding copyright information in digital image data, so that it is ensured that the copyright information will not be lost even after image processing such as format conversion or retouching is implemented on the image data. The copyright information embedded in the digital image data may be checked by executing an application program for identifying the electronic watermark constituting the copyright information on a personal computer or the like.
A plurality of methods for embedding an electronic watermark in image data have been proposed in correspondence to the following factors (1)˜(3) with regard to image data to be handled.
(1) The volume of information to be embedded in the image data;
(2) The level of editing tolerance which retains the information even after image processing such as format conversion is implemented on the image data as described above;
(3) The extent to which the quality of the image becomes degraded due to information embedding.
It is to be noted that in this specification, embedding an electronic watermark in image data is also referred to as superimposing an electronic watermark on image data. In other words, there are a plurality of methods employed to superimpose an electronic watermark on image data in the known art.
However, the following problems must be addressed when a plurality of methods for superimposing electronic watermarks are employed. In order to read copyright information written into digital image data, application programs for electronic watermark reproduction must be executed one at a time in correspondence to each of the plurality of methods for superimposing electronic watermarks to check the copyright information after first taking the digital image data into the personal computer. In particular, if different methods for superimposing electronic watermarks are employed for various sets of digital image data to be processed, a great length of time must be spent to check the copyright information and the verification operation becomes complicated. In addition, it is necessary to first create duplicate data by taking the image data to be processed into the personal computer without obtaining the copyright holder's consent, in order to check the copyright information.